The flight decks of U.S. Navy ships are a highly vital component for conducting war-time flight operations, training exercises, and the transportation of goods to fleet personnel. The surfaces of these decks are coated with a special material that provides a rough and abrasive profile so that aircraft, equipment, and sailors do not slide when a ship is maneuvering in the open waters. This material, known as a “non-skid” or “non-slip” coating, is located on approximately 4,000,000 square feet of flight deck area within the U.S. Navy, with carriers alone possessing a combined surface area of over 2,000,000 square feet of non-skid coating.
The Navy's current non-skid coatings are composed of two components that are mixed together and applied over an anti-corrosive deck primer using a phenolic roller. The coating is applied to the deck by a roller to create a rough ‘peak and valley’ profile, thereby providing a frictional surface to prevent the sliding, moving, or skidding of crew members, aircraft, storage containers, and machinery. To provide this aggressive profile, these coatings usually contain aluminum oxide or aluminum metal aggregate for general areas (Type-G) or landing areas (Type-L), respectively. Non-skid coatings have been used by the Navy for decades, yet their long-term performance continues to remain a highly contentious issue.
Conventional non-skid coatings are typically composed of aromatic epoxy resins (e.g., Bisphenol A, Bisphenol F, or Novolac) and amino-functional resins (e.g., amidoamine resin), along with fillers, colorizing pigments, and aggregates that are mixed together to create a viscous formula. Due to their inherent chemistry, traditional non-skid coatings are not durable to the external environment of UV and visible radiation, which is evident by the rapid fading, chalking, and degradation that is routinely observed within a few months after application. Traditional non-skid coatings also contain relatively high levels of volatile organic compounds (VOCs), usually as solvent(s), which can lead to solvent entrapment, shrinkage, and cracking as the coating cures. These problems, amongst others, can contribute to performance failures of non-skid coatings during routine operations, as exemplified by the loss of abrasive profile, lifting of coating from the deck due to loss of adhesion, or large areas of corrosion seepage that result from cracks in the non-skid coating.
Siloxane-based materials, which contain silicone-oxygen bonds, are becoming increasing popular within the global coatings market due to their outstanding external durability, chemical resistance, cleanability, increased thermal stability and low toxicity. Siloxane-based materials are also low in viscosity, thereby leading to reduced VOC requirements when formulated into coatings. Siloxanes can be engineered as linear or branched polysiloxane resins or cyclic structures (e.g., silsesquioxanes), and each can be functionalized with reactive organic groups.
Hybrid coating technology based on the incorporation of silicone-based resins (e.g., siloxanes or silanes) with epoxy or amine chemistries can provide better performance characteristics than traditional epoxy/amine coatings. For instance, silicone-oxygen bonds are much stronger than the carbon-carbon and carbon-hydrogen bonds that are typically found in traditional non-skid coatings. This increased bond strength leads to a greater external durability and chemical resistance, thereby extending the life-cycle of a coating by preventing the rapid chalking, fading and/or cracking that occurs due to degradation by ultra-violet (UV) and visible radiation. On the other hand, the organic portions of a hybrid coating are used to provide substrate binding and flexibility, thus leading to a coating that possesses direct-to-metal (DTM) adhesion and does not require a primer.
Silsesquioxanes are low in VOCs, provide good hardness and external durability, and can be functionalized with pendant reactive groups. Amino-functional silsesquioxane resins are commercially available and were used to formulate non-skid coatings as a replacement for the traditional amine resins (e.g., amidoamines) that often cause yellowing. As for the epoxy component, the traditional aromatic epoxies have been replaced with non-aromatic epoxy resins (e.g., zero VOC cycloaliphatic epoxies). These epoxy resins yield similar hardness and performance, yet provide better external durability due to their lack of aromatic character.
Thus, it is desirable to have a non-skid coating that has greater exterior durability than conventional coatings.